The present invention, in some embodiments thereof, relates to a wireless point-to-point communication system, and, more particularly, but not exclusively, to a single-carrier modulation scheme with a continuous transmission.
Wireless point-to-point communication systems are deployed all over the world, for example as a backbone of cellular networks and wireless Internet services. The wireless point-to-point communication systems usually require a Line-Of-Sight (LOS) and use a regulated frequency band, in order to ensure high availability with little or no interference. A required bit-error-rate in such links is typically below 10−13. Frequency bands used in such regulated communication systems are commonly in the range of 7 GHz to 38 GHz.
Since communication happens between two specific nodes in a network, transmission beams are generated using dish antennas which focus the transmission beams, which provide a receiver with a stronger signal and less interference than unfocused transmissions. The focused beams cause interference with other wireless links which use the same frequency when the beams are also in a similar direction.
For purposes of better understanding some embodiments of the present invention, as illustrated in FIGS. 2A, 2B, 3, 4A, 4B, 5, 6, 7A, 7B, and 8 of the drawings, reference is first made to FIG. 1A, which is a simplified illustration of a tree network 100 scenario in which an aggregation point 110 communicates with two tail sites 115 116 via two communication links 113 114.
Such a scenario is termed a tree network, in which the tail sites 115 116 are tree “leaves”. An angular separation 111 between the two tail sites 115 116 is too small for using the same frequency on the two communication links 113 114. When the same frequency is used, the interference between the two communication links 113 114 is in both directions, i.e., from the aggregation point 110 to the tail sites 115 116 and from the tail sites 115 116 to the aggregation point 110.
In such a case, different frequencies have to be used on the two communication links 113 114. Frequencies are usually regulated, and obtaining frequencies is very expensive. If no communication frequencies are available, wireless communication cannot be established, and expensive alternatives should be considered, such as, by way of a non-limiting example, laying a land line.
The example above describes an aggregation point 110 communicating with two tail sites 115 116. However, some applications may include network rings which do not necessarily involve an aggregation point.
Reference is now made to FIG. 1B, which is a simplified illustration of a ring network 120 scenario in which the ring network includes several nodes 125 126 127 128 129. The nodes 125 126 127 128 129 are connected by communication links 140 141 142 143 144.
Angular separations 130, 132, and 133 between the communication links 140 144, 141 142, and 142 143 respectively, are too small for using a same frequency on the pairs of communication links 140 144, 141 142, and 142 143 respectively.
Angular separations 131 and 134 between the communication links 140 141 and 143 144 respectively, are close to 180°. At such angles if a same frequency is used on the pairs of communication links, the pairs of communication links 140 141 and 143 144 may interfere. For example, node A 125 may receive both communications via the communication link 140 from node B 126 and interference from the communication link 141 from node C 127.
In such a case also, different frequencies have to be used on the interfering communication links.
It is noted that FIG. 1B depicts a ring with all communication links having potentially problematic angles. Many rings may have some communication links with problematic angles, and some without.
It is noted that both the ring network 120 and the tree network 100 with an aggregation point are common scenarios.
Additional background art includes:
Rizaner A., Amca H. A., Hacioglu K., Ulusoy A. H., “Channel Estimation using Short Training Sequences”, IEEE 52nd Vehicular Technology Conference, 2000, Vol. 6, pp. 2630-2633.
Miao Lu, Bo Chen, Xiaolin Hou, Xin Zhang, Dongmei Luo, “A Data Aided Channel Estimation Method Based on CAZAC”, IEEE 68th Vehicular Technology Conference, 2008, pp. 1-5.
Raja Rajeswari K., Gangatharan N., Morris G. E., Radhakrishna Rao G. S. V., Visvesvara Rao B., Swamy, G. N., “Channel Estimation from Known Preamble Sequences”, The 8th International Conference on Communication Systems, 2002. ICCS 2002, Vol. 1, pp. 270-273